An internal auditor wants to detect at least one irregularity when the occurrence rate is very low; which sampling method is most appropriate?

• A. Sequential sampling
• B. Variable estimation sampling
• C. Attribute estimation sampling
• D. Discovery sampling

Answer: (D)

When the goal is to detect at least one irregularity in a population where the occurrence rate is very low, the sampling approach should be built around discovery of a rare event rather than estimating how many exist. Discovery sampling is designed for this exact situation: it concentrates on finding a single irregularity and sets the sample size to maximize the chance of uncovering at least one if any irregularities are present. Once a defect is found, the audit can proceed accordingly; if none are found within the plan, you can draw conclusions based on the predefined detection rules. Other methods focus on estimating proportions or means or on stopping rules based on results, rather than prioritizing the chance of discovering a rare irregularity.